Safety of inter-facility transport strategies for patients referred for severe acute respiratory distress syndrome

Background Inter-facility transport of patients with acute respiratory distress syndrome (ARDS) in the prone position (PP) is a high-risk situation, compared to other strategies. We aimed to quantify the prevalence of complications during transport in PP, compared to transports with veno-venous extracorporeal membrane oxygenation (VV-ECMO) or in the supine position (SP). Methods We performed a retrospective, single center cohort study in Lyon university hospital, France. We included patients ≥ 16 years with ARDS (Berlin definition) transported to an ARDS referral center between 01/12/2016 and 31/12/2021. We compared patients transported in PP, to those transported in SP without VV-ECMO, and those transported with VV-ECMO (in SP), by a multidisciplinary and specialized medical transport team, including an emergency physician and an intensivist. The primary outcome was the rate of transport-related complications (hypoxemia, hypotension, cardiac arrest, cannula or tube dislodgement) in each study groups, compared using a Fisher test. Results One hundred thirty-four patients were enrolled (median PaO2/FiO2 70 [58–82] mmHg), of which 11 (8%) were transported in PP, 44 (33%) with VV-ECMO, and 79 (59%) in SP. The most frequent risk factor for ARDS in the PP group was bacterial pneumonitis, and viral pneumonitis in the other 2 groups. Transport-related complications occurred in 36% (n = 4) of transports in PP, compared to 39% (n = 30) in SP and 14% (n = 6) with VV-ECMO, respectively (p = 0.33). VV-ECMO implantation after transport was not different between SP and PP patients (n = 7, 64% vs. n = 31, 39%, p = 0.19). Conclusions In the context of a specialized multi-disciplinary ARDS transport team, transport-related complication rates were similar between patients transported in PP and SP, while there was a trend of lower rates in patients transported with VV-ECMO. Supplementary Information The online version contains supplementary material available at 10.1186/s12873-023-00901-y.

Patients on VV-ECMO were ventilated using quasi-apneic ventilation (volume-controlled mode, tidal volume 1 ml.kg -1 PBW, PEEP to maintain end-inspiratory airway pressure between 20 and 25 cmH2O, respiratory rate 5 bpm, I:E ratio of 1:2) or ultra-protective ventilation (pressure controlled mode, PEEP 14 cmH2O, inspiratory pressure 22 cmH2O, respiratory rate 5 bpm, I:E ratio of 1:2).VV-ECMO was set with the following parameters: equal FiO2 and FmO2 (sweep gas O2 fraction) set at 1, pump flow corresponding to at least 60% of the patient's measured cardiac output and adjusted to keep the SpO2 > 88% and PaO2 > 55 mmHg, sweep gas flow equal to the pump flow and adjusted to maintain the arterial CO2 partial pressure (PaCO2) below 45 mmHg.

Patients without VV-ECMO
After transport to the ARDS referral center, patients without VV-ECMO were managed following the most recent French and international ARDS recommendations, including protective ventilation, PEEP titration and weaning, neuromuscular blocking agents administration and PP 3,4 .Patients were placed under VV-ECMO if eligible using the same criteria as given above.Mechanical ventilation weaning was assessed daily, by mean of a spontaneous breathing trial, after PEEP weaning in conscious patients with a FiO2 ≤ 50%.

Patients with VV-ECMO
Patients under VV-ECMO were ventilated with quasi-apneic ventilation, using the same strategy as given above.VV-ECMO blood and sweep gas flows were adjusted based on the following parameters: SpO2 between 88 and 92%, PaO2 between 55 and 80 mmHg, PaCO2 < 45 mmHg, pH > 7.20.VV-ECMO weaning was assessed daily, by turning off the sweep gas flow to 0 L.min -1 and resuming conventional protective ventilation settings.If the test was positive (based on a PaO2/FiO2 ratio > 150 mmHg after 2h, and a driving pressure < 15 cmH2O at VT 6 ml.kg -1 PBW), VV-ECMO was withdrawn on the same day.

Supplemental Methods 4. Data collection
The pre-transport data were taken from the digital file transmitted by the addressing ICU.
The per-and post-transport data were collected from the patient's electronic medical record.
We identified demographics and comorbidities at baseline, as well as ARDS risk factors and severity, respiratory mechanics and physiology, ARDS therapeutics, SOFA scores, and hospital and ICU mortalities at baseline and during follow-up.Follow-up ended at patient's date of hospital discharge, ICU discharge or death, whichever occurred last.
ARDS class was defined based on the worst PaO2/FiO2 ratio measured on transport day prior to transport.Oxygenation response to PP was defined by an increase > 20 mmHg in PaO2/FiO2 ratio between SP and PP at any time on transport day.Data regarding VV-ECMO settings and management (including post-transport implantation) were collected at the same time points.
In case of a missing PaO2, it was estimated from the SpO2, using the EPIC-II trial concordance table 5 .Likewise, in case of missing SpO2, it was estimated from the PaO2.The driving pressure was calculated as the difference between the end-inspiratory airway pressure and the total PEEP if measured; else, the set PEEP was used for its computation.All variables were defined in the case report form, except for those identified with one or more *.*: defined a posteriori using the worst PaO2/FiO2 value measured on transport day, prior to transport; **: defined a posteriori using the combination of the worst PaO2/FiO2 value measured on transport day with the PaO2/FiO2 value measured closest to transport, both being prior to transport; ***: defined a posteriori, using the combination of vasopressor administration and an arterial lactate concentration > 4 mmol.L -1 ; †:denominator is the number of patients with a theoretical ECMO indication and o contra-indications.p-values examines the difference between groups using a Fisher test.FiO2: inspired fraction in O2; PaO2: arterial partial pressure in O2; SOFA: sepsis-related organ failure assessment; VV-ECMO: veno-venous extracorporeal membrane oxygenation

Table 2 .
ARDS risk factorsData is shown as count (percentage).Missing values were not imputed.Percentage are reported to the whole number of observations of the column, including missing values.p values examines the difference between groups, using a Fisher test.A post-hoc analysis with pairwise comparison (using a logistic regression model) was performed if the p value of the Fisher test was < 0.20.*: p<0.05 in post hoc analysis between the PP group and the VV-ECMO group; †:p<0.05 in post hoc analysis between the PP group and the SP group.ARDS: acute respiratory distress syndrome; VV-ECMO: veno-venous extracorporeal membrane oxygenation; PP: prone position; SP: supine position Supplemental

Table 3 .
Theoretical indications and potential contra-indications for VV-ECMO in patients transported in the prone or supine position without VV-ECMO Count and percentage are reported to the whole number of observations of the column, including missing values.